Does anyone remember if the Parker-Hale M98 trigger, with the bolt locking side safety, requires receiver modifications to mount on a military issue receiver?

Yes there is a mod to the receiver. A small slot was made with an EDM machine that allowed a small lever to come up and block the bolt.

Thanks Snowman. I found a good P-H trigger at a bargain, but installation sounds like something you can't do on a mill.

I'm not familiar with the Parker Hale trigger. However I have used a number of Mark X triggers on 98 without any trouble. On the Mark X the safety lever has a little tab on the front of it designed to stick up though action and lock the bolt. I remove the tab. This also allows unloading the rifle without taking the gun off safe. I've done it on a number of Mark Xs as well when a locking bolt is not wanted.